1. Field of the Invention
The invention relates to collet surface structures, and more particularly, to a collet surface structure which eliminates leakage-oil on the hydraulic clamping system of an hydraulic highspeed press.
2. Discussion of the Related Art
Hydraulic high-speed presses are well known, for example, from German Offenlegungsschrift 3,637,544 German Offenlegungsschrift 3,637,545. By means of a special construction and control employed in these presses, a virtually jolt-free and wear-free coupling is obtained. Specifically, these presses use a non-positive clamping under low effective masses of the pressure rods synchronously with the movement of the press. This is made possible by hydraulic damping and automatic compensation of the connected masses by prestressed pressure pads. The neutralization of the weight of the pressure rods and pistons leads to shorter braking times, a higher speed for the negotiable idle-stroke distance and high closing speeds. The diaphragms which are used in this construction, for example nylon sleeves, are secured at each end by means of two O-ring seals to prevent the escape of high-pressure oil into the clamping region of the collets and pressure rods.
If an O-ring seal becomes leaky, highpressure oil flows into the clamping region uncontrollably and causes a reduced non-positive connection between the collets and the pressure rods. Collet systems of this type will not clamp in a slip-free way if, as a result of an uncontrolled film of lubricating oil, a hydrostatic film forms between the pressure rod and collet, because then the oil film cannot be broken down. In other words, the oil cannot be eliminated within the desired clamping time of approximately 0.5 to 1 second.
Normally, because of the prevailing frictional conditions a sufficient non-positive connection is provided, even under lubrication. Slipping nevertheless occurs due to such uncontrolled leakages, because a hydrostatic film is formed on which the collet will slide briefly against the pressure rod, until this hydrostatic film is forced away. When this occurs, local friction temperatures become very high, thereby causing this oil to crack with a resulting slipping over approximately 20 to 30 mm. The cracked oil settles as a coating on the pressure rods and thus leads to further uncontrolled frictional conditions. As a result, the entire system will fail, so that the press must be stopped and taken out of production.